Methods and compositions for improved oxygen scavenging

ABSTRACT

A composition capable of scavenging oxygen composed of (i) a copolymer having long chain branches comprising units derived from monomers of ethylene and at least one vinyl unsaturated alicyclic monomer; (ii) a transition metal catalyst; (iii) preferably, with a photoinitiator; and (iv) optionally, a polymeric diluent.

A division of application Ser. No. 08/942,266 filed Oct. 1, 1997, nowU.S. Pat. No. 5,981,676.

FIELD OF THE INVENTION

The invention generally relates to compositions, articles and methods ofscavenging oxygen in environments containing oxygen-sensitive products,particularly food and beverage products. More specifically, the presentinvention is directed to oxygen scavenger compositions composed ofcopolymers having long chain branching derived from monomers of ethyleneand a vinyl unsaturated alicyclic compound, a transition metal compoundand, optionally, a photoinitiator compound. The subject composition canbe readily formed into films or blended with other film forming polymersto provide an improved oxygen scavenger packaging material. As will beevident from the disclosure below, the term "oxygen scavenger" or"scavenger" refers to materials which consume, deplete or reduce theamount of oxygen from a given environment.

BACKGROUND OF THE INVENTION

It is well known that limiting the exposure of oxygen-sensitive productsto oxygen maintains and enhances the quality and "shelf-life" of theproduct. For instance, by limiting the oxygen exposure of oxygensensitive food products in a packaging system, the quality of the foodproduct is maintained, and food spoilage is avoided. In addition, suchpackaging also keeps the product in inventory longer, thereby reducingcosts incurred from waste and having to restock. In the food packagingindustry, several means for limiting oxygen exposure have already beendeveloped. At present, the more commonly used means include modifiedatmosphere packaging (MAP), vacuum packaging and oxygen barrier filmpackaging. In the first two instances, reduced oxygen environments areemployed in the packaging, while in the latter instance, oxygen isphysically prevented from entering the packaging environment.

Another, more recent, means for limiting oxygen exposure involvesincorporating an oxygen scavenger into the packaging structure.Incorporation of a scavenger in the package can provide a uniformscavenging effect throughout the package. In addition, suchincorporation can provide a means of intercepting and scavenging oxygenas it is passing through the walls of the package (herein referred to asan "active oxygen barrier"), thereby maintaining the lowest possibleoxygen level throughout the package.

One example of an oxygen scavenger incorporated into an oxygenscavenging wall is illustrated in European Applications 301,719 and380,319 as well as in PCT 90/00578 and 90/00504. See also U.S. Pat. No.5,021,515. The oxygen scavenger disclosed in these patent applicationscomprises polyamide/transition metal catalyst compositions. Throughcatalyzed scavenging by the polyamide, the package wall regulates theamount of oxygen which reaches the interior of the package (activeoxygen barrier). However, it has been found that the onset of usefuloxygen scavenging, i.e. up to about 5 cubic centimeters (cc) oxygen persquare meter per day at ambient conditions, may not occur for as long as30 days and, therefore, is not acceptable for many applications.

Further, in regards to the incorporation of the polyamide/catalystsystem into the packaging material, polyamides are typicallyincompatible with the thermoplastic polymers, e.g., ethylene-vinylacetate copolymers and low density polyethylenes, typically used to makeflexible packaging materials and films. Even further, when polyamidesare used by themselves to make a flexible package wall, they usuallyresult in inappropriate stiff structures. Polyamides are also moredifficult to process when compared with thermoplastic polymers typicallyused to make flexible packaging.

U.S. Pat. No. 5,399,289 discloses oxygen scavenger compositions composedof ethylenically unsaturated hydrocarbon polymers and transition metalcatalysts. The polymers are required to have a low ethylenic double bondcontent of from 0.01 to 10 equivalents per 100 grams of polymer so as toprovide a product with both scavenging properties and retained physicalproperties. Various conventional homopolymers, copolymers and polymerblends are disclosed. Because these polymers are amorphous materialsthey are difficult to blend and be processed with film formingsemi-crystalline polymers, such as low density polyethylene and thelike, which are conventionally used in providing flexible films and thelike for packaging applications.

U.S. Pat. No. 5,211,875 also discloses the use of ethylenicallyunsaturated compounds in conjunction with a transition metal as well asa photoinitiator to facilitate initiation of the effective scavengingactivity. The ethylenically unsaturated polymers and copolymerssuggested by this reference are also amorphous materials and, therefore,have low compatibility with conventional film forming polymers, such aspolyethylenes. Because of the limited compatibility of the scavengerpolymer with the film forming polymer, one is required to limit theamount of scavenger polymer in the blend and is usually confronted witha resultant composition which is difficult to process.

It is highly desired to have an oxygen scavenger composition which iscomposed of a polymeric material having high processability which can bedirectly formed into films useful in the packaging field or have highcompatibilty with semi-crystalline polyolefins and provide a highlyprocessable blend with such polymeric materials having known utility forpackaging application.

Further, it is highly desired to have a film or composition composed ofan ethylenically unsaturated polymer capable of scavenging oxygen whichcan substantially retain its physical properties after significantoxygen scavenging.

Still further, it is highly desired to provide an oxygen scavengercomposition which does not provide, upon oxygen scavenging, by-productformation which can detract from the color, taste or odor of thepackaged product.

SUMMARY OF THE INVENTION

The present invention is directed to oxygen scavenger compositionscomposed of (i) a copolymer having long chain branches comprising unitsderived from monomers of ethylene and at least one vinyl unsaturatedalicyclic monomer; (ii) a transition metal catalyst; (iii) preferablyfurther with a photoinitiator; and (iv) optionally, a polymeric diluent.

The present composition has been found to exhibit a high degree ofprocessability to form film products; to be highly compatible withconventional polymers used in forming films, such as semi-crystallinepolyolefins and the like; to exhibit significant ability to scavengeoxygen while part of a film or article used in forming a package foroxygen sensitive products; and to not produce significant by-productswhich would detract from the packaged product's odor, color and/ortaste.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is directed to an oxygen scavenger compositioncomposed (i) of at least one copolymer having long chain branchescomprising units derived from ethylene and at least one vinylunsaturated alicyclic comonomer; (ii) a transition metal catalyst; (iii)preferably further with a photoinitiator; and (iv) optionally, with apolymeric diluent. The present long chain branched copolymer issemi-crystalline to a sufficient degree to be highly compatible withpolyolefins and the like conventionally used to provide packaging filmsand laminated structures and to provide a composition or blends whichhas high processability, e.g., low susceptibility to melt fracture evenunder high shear stress conditions such as encountered in extrusionprocessing.

The novel copolymers found useful in the present invention are fullydescribed in copending U.S. application Ser. No. 08/941,261,concurrently filed with the instant application. The teachings of saidcopending application are incorporated herein by reference in itsentirety.

Processability has been attributed to the structural feature of thepresence of long chain branching along the subject copolymer's chain aswell as its low molecular weight distribution. Molecular weightdistribution or polydispersity of a polymer (the ratio of weight averagemolecular weight (Mw) to number average molecular weight (Mn) is aninfluence on the processability. Thus, polymers having a low ratio ofMw/Mn and a high ratio of melt flow index (I₁₀ /I₂) conducted atdifferent loads (10 Kg and 2 Kg), as described in ASTM D-1238 areindicative of a polymer structure having long chain branching and, inturn, are known to provide desired processability characteristics.

The present oxygen scavenger composition has, as an active scavengeragent, a long chain branched (having branch chains of ≧6 carbon atoms)containing copolymer of ethylene and at least one vinyl unsaturatedalicyclic group containing comonomer represented by the formula:##STR1## where ##STR2## represents a C₆ -C₁₂ ethylenically unsaturatedalicyclic group which may further have one or more of its hydrogen atomsof the alicyclic group substituted by a C₁ -C₁₂ hydrocarbon, as fullydescribed below.

The subject copolymer must have ethylene as one of its monomeric forminggroups. In addition, the subject copolymer must have, as one of itsmonomeric forming groups, at least one monomer of formula I, above. Thismonomer must have (i) a hydrogen atom pendent from the beta carbon andthe gamma carbon of the monomer I; (ii) an alicyclic, gamma carbon atomcontaining group pendent from the beta carbon; (iii) at least onenon-aromatic, ethylenic carbon--carbon double bond within the alicyclicgroup.

The alicyclic, gamma carbon atom containing group is selected from anunsaturated (non-aromatic) C₆ -C₁₂ alicyclic group such as, for example,2-cyclohexenyl, 3-cyclohexenyl, 2,5-cyclohexadienyl, 2-cyclooctenyl,3-cyclooctenyl, 4-cyclcooctenyl, 2,6-cyclooctadienyl, cyclododecatrienyland the like. The alicyclic groups, besides having ethylenicunsaturation within the alicyclic group, can have one or more C₁ -C₂₀hydrocarbon group substitution pendent from the alicyclic ring providedthe gamma carbon atom has a pendent hydrogen atom. The substitution canbe an aliphatic hydrocarbon, such as, for example, methyl, ethyl,isopropyl, pentyl and the like; an alkenyl group such as, for example,3-butenyl, 4-hexenyl and the like; or a saturated or unsaturatedalicyclic group which may be fused or unfused to the gamma carbon atomcontaining alicyclic ring.

The subject copolymer may, in addition to the monomers of ethylene andmonomer I described above, contain at least one additional monomer otherthan those defined above. For example, the additional monomer may be aC₃ -C₂₀ alpha-olefin such as propylene, 1-butene, 1-hexene, 3-methylbutene-1, 1-octene 4-methyl pentene and the like; cycloolefins such as,for example, cyclopentene, norbornene, tetracyclododecene and the like;and non-conjugated dienes such as, for example,5-ethylidene-2-norbornene, 5-vinyl-2-norbornene,5-methylene-2-norbornene, 2,5-norbornadiene 1,3-divinylcyclohexane,1,4-divinyl cyclohexane, 1-allyl-5-vinylcyclooctane, dicyclopentadiene,1,4-hexadiene, 1,7-octadiene and the like.

Ethylene must be a comonomer forming the subject copolymer. It can bepresent in from about 0.01 to about 99 molar percent of the copolymer,preferably from 25 to 95 molar percent and most preferably from 75 to 90molar percent of the copolymer formed.

The monomer I must be a comonomer forming the subject copolymer. It canbe selected from one or from a mixture (in any proportion) of more thanone monomer I. It can be present in from about 1 to about 35 molarpercent of the copolymer, preferably from about 1 to 15 and mostpreferably from about 1 to 10 molar percent of the copolymer formed.

The remainder of the subject copolymer can be formed from othercopolymerizable monomeric compounds, as described above.

The resulting copolymer has been found to have a narrow molecular weightdistribution and long chain branches as evidenced by its lowpolydispersity (Mw/Mn) and by its high melt flow index ratio (I₁₀ /I₂).Its polydispersity normally has a value of at least about 1.5 to about 5and preferably at least about 1.7 to about 2.5 and most preferably 1.9to 2.5. In combination, in polymers of low polydispersity, a long chainbranched structure is shown to be present by the high values of meltflow index ratio of at least about 8 and preferably 8.5, and morepreferably at least about 10, as measured in accordance with ASTMD-1238.

The preferred copolymers of the present invention comprises unitsderived from comonomers of ethylene and at least one vinyl alicyclicmonomer wherein the alicyclic ring contains one ethylenic carbon--carbondouble bond as represented by the formula: ##STR3## wherein n and m areeach independently selected from positive integers of 0 to 9, providedthat the sum of n+m has a value of from 3 to 9 and more preferably from3 to 5.

The most preferred copolymer of the instant invention is formed from thecomonomers of ethylene and vinyl cyclohexene. This copolymer preferablyhas from about 1 to about 35 mole percent vinyl cyclohexene preferablyfrom about 1 to 10 and most preferably from about 2 to 8 mole percent ofvinyl cyclohexenes (which can be determined by carbon-13 nuclearmagnetic resonance analysis).

The weight average molecular weight of the subject copolymers will varydepending on the particular monomer I present, the amount of saidmonomer I present in the copolymer as well as the particular catalystused in its formation. Normally, the weight average molecular weightwill range from about 10,000 to 1,000,000, with from about 25,000 to125,000 being preferred. Regulating the molecular weight can beaccomplished by having hydrogen present in the polymerization reactionvessel during the formation of the subject long chain branchedcopolymer.

It has been unexpectedly found that the subject long chain branchedcopolymer can be formed by solution polymerization utilizing certainbridged substantially unstrained metallocene catalysts, as fullydescribed in copending U.S. application Ser. No. 08/941,261 whichteaching has been incorporated herein by reference. The solvent formingthe polymerization media can be an inert (with respect to the comonomerspresent) liquid hydrocarbon, which may be, for example, a C₄ -C₁₀aliphatic hydrocarbon such as, for example, isobutane, pentane,isopentane or the like or mixtures thereof; or an aromatic hydrocarbon,such as, for example, benzene, toluene, xylene or the like. Alternately,the solvent may be one or more of the monomers I or, if appropriate, thethird comonomer present in excess either alone or further with an inertdiluent, such as those solvents described above. Where a comonomer isused as a solvent for the polymerization, it is preferred that it beselected from a monomer I.

The subject oxygen scavenger composition requires the presence of atransition metal compound, as a scavenger catalyst, in combination withthe long chain branched copolymer described above.

The transition metal catalyst may be a salt of a metal selected from thefirst, second or third transition series of the Periodic Table andpreferably those of the series from scandium to zinc (i.e., Sc, Ti, V,Cr, Mn, Fe, Co, Ni, Cu and Zn) with preferably iron, nickel or copperand manganese being more preferred and cobalt being most preferred.Suitable counterions for the metal include, but are not limited to,chloride, acetate, oleate, stearate, palmitate, 2-ethylhexanoate,neodecanoate or naphthenate. Particularly preferable salts includecobalt (II) 2-ethylhexanoate, cobalt oleate and cobalt (II)neodecanoate. The metal salt may also be an ionomer, in which case apolymeric counterion is employed. Such ionomers are well known in theart.

The subject composition when used in forming a packaging article can becomposed solely of the above described long chain branched copolymer andtransition metal catalyst. However, components such as photoinitiatorscan be added to further facilitate and control the initiation of oxygenscavenging properties. For instance, it is often preferable to add aphotoinitiator, or a blend of different photoinitiators, to the oxygenscavenger compositions, especially when antioxidants are included toprevent premature oxidation of that composition during processing.

Suitable photoinitiators are well known to those skilled in the art asexemplified by the teachings of WO 97/07161 and copending U.S.application Ser. No. 08/857,226, filed May 16, 1997, which isincorporated herein in its entirety by reference. Specific examplesinclude, but are not limited to, benzophenone, o-methoxy-benzophenone,acetophenone, o-methoxy-acetophenone, acenaphthenequinone, methyl ethylketone, valerophenone, hexanophenone, α-phenyl-butyrophenone,p-morpholinopropiophenone, dibenzosuberone, 4-morpholinobenzophenone,benzoin, benzoin methyl ether, 4-o-morpholinodeoxybenzoin,p-diacetylbenzene, 4-aminobenzophenone, 4'-methoxyacetophenone,substituted and unsubstituted anthraquinones, α-tetralone,9-acetylphenanthrene, 2-acetyl-phenanthrene, 10-thioxanthenone,3-acetyl-phenanthrene, 3-acetylindole, 9-fluorenone, 1-indanone,1,3,5-triacetylbenzene, thioxanthen-9-one, xanthene-9-one,7-H-benz[de]anthracen-7-one, benzoin tetrahydropyranyl ether,4,4'-bis(dimethylamino)-benzophenone, 1'-acetonaphthone,2'-acetonaphthone, acetonaphthone and 2,3-butanedione,benz[a]anthracene-7,12-dione, 2,2-dimethoxy-2-phenylacetophenone,αα-diethoxy-acetophenone, αα-dibutoxyacetophenone, etc. Singlet oxygengenerating photosensitizers such as Rose Bengal, methylene blue, andtetraphenyl porphine may also be employed as photoinitiators. Polymericinitiators include poly(ethylene carbon monoxide) andoligo[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]propanone]. Use of aphotoinitiator is preferable because it generally provides faster andmore efficient initiation. When actinic radiation is used, theinitiators may also provide initiation at longer wavelengths which areless costly to generate and less harmful.

When a photoinitiator is used, its primary function is to enhance andfacilitate the initiation of oxygen scavenging upon exposure toradiation. The amount of photoinitiator can vary. In many instances, theamount will depend on the amount and type of monomer I present in theinstant invention, the wavelength and intensity of radiation used, thenature and amount of antioxidants used, as well as the type ofphotoinitiator used. The amount of photoinitiator also depends on howthe scavenging composition is used. For instance, if thephotoinitiator-containing composition is placed underneath a layer whichis somewhat opaque to the radiation used, more initiator may be needed.For most purposes, however, the amount of photoinitiator, when used,will be in the range of 0.01 to 10% by weight of the total composition.The initiating of oxygen scavenging can be accomplished by exposing thepackaging article to actinic or electron beam radiation, as describedbelow.

Antioxidants may be incorporated into the scavenging compositions ofthis invention to control degradation of the components duringcompounding and shaping. An antioxidant, as defined herein, is anymaterial which inhibits oxidative degradation or cross-linking ofpolymers. Typically, such antioxidants are added to facilitate theprocessing of polymeric materials and/or prolong their useful lifetime.Although such additives prolong the induction period for oxygenscavenging activity to occur in the absence of irradiation, when thelayer's or article's scavenging properties are required, the layer orarticle (and any incorporated photoinitiator) can be exposed toradiation.

Antioxidants such as 2,6-di(t-butyl)-4-methyl-phenol(BHT),2,2'-methylene-bis(6-t-butyl-p-cresol), triphenylphosphite,tris-(nonylphenyl)phosphite and dilaurylthiodipropionate would besuitable for use with this invention.

When an antioxidant is included as part of the present composition, itshould be used in amounts which will prevent oxidation of the scavengercomposition's components as well as other materials present in aresultant blend during formation and processing but the amount should beless than that which would interfere with the scavenging activity of theresultant layer, film or article after initiation has occurred. Theparticular amount needed will depend on the particular components of thecomposition, the particular antioxidant used, the degree and amount ofthermal processing used to form the shaped article, and the dosage andwavelength of radiation applied to initiate oxygen scavenging and can bedetermined by conventional means. Typically, they are present in about0.01 to 1% by weight.

The present copolymer has been found to provide a film which is suitableas a packaging material. The present copolymer can be used as the solepolymeric material forming at least one layer of a film (the film may bea multilayer film having, for example, a gas barrier layer, a seallayer, etc.). Alternately, the subject copolymer containing compositioncan further comprise one or more non-oxygen scavenger diluent polymersknown to be useful in packaging film forming materials. Such polymersare thermoplastic and render the film more adaptable for use aspackaging layers. Suitable diluent polymers include, but are not limitedto, polyethylene, low density polyethylene, very low densitypolyethylene, ultra-low density polyethylene, high density polyethylene,polyethylene terephthalate (PET), polyvinyl chloride, and ethylenecopolymers such as ethylene-vinyl acetate, ethylene-alkyl(meth)acrylates, ethylene-(meth)acrylic acid and ethylene-(meth)acrylicacid ionomers. In rigid articles such as beverage containers PET isoften used. Blends of different diluent polymers may also be used.Generally, these polymers are semi-crystalline materials useful informing packaging materials and films. The selection of the polymericdiluent largely depends on the article to be manufactured and the enduse thereof. Such selection factors are well known in the art. Forinstance, certain polymers are known to provide clarity, cleanliness,barrier properties, mechanical properties and/or texture to theresultant article.

Other additives which may also be included in oxygen scavenger layersinclude, but are not necessarily limited to, fillers, pigments,dyestuffs, stabilizers, processing aids, plasticizers, fire retardants,anti-fog agents, etc.

The amounts of the components which are used in the oxygen scavengingcompositions, or layers have an effect on the use, effectiveness andresults of this method. Thus, the amounts of copolymer, transition metalcatalyst and any photoinitiator, antioxidant, polymeric diluents andadditives, can vary depending on the article and its end use.

For instance, one of the primary functions of the long chain branchedcopolymer described above is to react irreversibly with oxygen duringthe scavenging process, while the primary function of the transitionmetal catalyst is to facilitate this process. Thus, to a large extent,the amount of copolymer present will affect the oxygen scavengingcapacity of the composition, i.e., affect the amount of oxygen that thecomposition can consume. The amount of transition metal catalyst willaffect the rate at which oxygen is consumed. Because it primarilyaffects the scavenging rate, the amount of transition metal catalyst mayalso affect the induction period.

It has been found that the subject long chain branched copolymers, whenused as part of the subject composition, provide oxygen scavengerproperties at desirable rate and capacity while causing the compositionto have enhanced processability and compatibility properties overconventional ethylenically unsaturated polymers. Thus, the presentcomposition can be used to provide, by itself or as a blend with diluentfilm forming polymers, such as polyolefins and the like, a packagingmaterial or film having enhanced processability properties. Further, itis believed that the subject oxygen scavenger composition consumes anddepletes the oxygen within a package cavity without detracting from thecolor, taste and/or odor of the product contained within the packagecavity.

The amount of copolymer of the subject composition may range from 1 to99%, preferably from 10 to 90%, by weight of the composition or layercomposed of said composition in which both copolymer and transitionmetal catalyst are present (hereinafter referred to as the "scavengingcomposition", e.g., in a coextruded film, the scavenging compositionwould comprise the particular layer(s) in which both the copolymer andtransition metal catalyst components are present together). Typically,the amount of transition metal catalyst may range from 0.001 to 1% (10to 10,000 ppm) of the scavenging composition, based on the metal contentonly (excluding ligands, counterions, etc.). In the event the amount oftransition metal catalyst is less than 1%, it follows that the copolymerand any additives will comprise substantially all of the remainder ofthe composition.

Alternately, when one or more diluent, substantially non-scavengerpolymers are used as part of the composition, those polymers cancomprise, in total, as much as 99%, preferably up to 75% by weight ofthe scavenging composition with the subject copolymer and transitionmetal catalyst and, if appropriate, photoinitiator, present in ratiosdescribed above.

Any further additives employed normally will not comprise more than 10%of the scavenging composition, with preferable amounts being less than5% by weight of the scavenging composition.

The oxygen scavenger composition of the present invention unexpectedlycan have enhanced properties not achievable by conventionalcompositions. Firstly, the copolymer of the present composition can havea high content of unsaturation due to the high molar content of vinylalicyclic units in the copolymer and/or the ability to form filmssuitable for packaging applications directly from thecopolymer/transition metal composition. Further, the present compositionmay have a high content of copolymer scavenger agent even when thecomposition contains a diluent polymer. As stated above, the longbranched chain copolymer is highly compatible with known film formingpolymers, such as polyolefins and in particular semi-crystallinepolymers conventionally used in providing film packaging articles.Because of the high compatibility, the copolymer and other diluentpolymer can be readily blended in any ratio. In contrast, prior usedamorphous ethylenically unsaturated polymers, do not readily providehigh content blends which are suitable for processing (e.g., extruded)into films and the like. Still further, the present composition, whetherformed with or without a diluent polymer, has been found to have highprocessability, that is to have high zero-shear viscosity, lowpropensity to melt-fracture, high melt tension and a long relaxationtime under melt conditions. Thus, the present copolymer can be readilyprocessed (e.g., extruded) at high rates into films having highlydesired characteristics (e.g., high clarity, reduced surfaceimperfections at high extrusion rates) alone or as a layer of amulti-ply film.

As indicated earlier, the composition of the present invention can beused as a single scavenging layer or a scavenging layer present in amultilayer film or in forming other articles for container application.Single layered articles can be readily prepared by extrusion processing.Multilayered articles are typically prepared using coextrusion, coating,lamination or extrusion/lamination, as taught in U.S. Pat. Nos.5,350,622 and 5,529,833. The additional layers of a multilayered articlemay include "oxygen barrier" layers, i.e. those layers of materialhaving an oxygen transmission rate equal to or less than 500 cubiccentimeters per square meter per day per atmosphere (cc/m² -d.atm) atroom temperature, i.e. about 25° C. Typical oxygen barriers comprisepoly(ethylene/vinylalcohol), poly(vinylalcohol), polyacrylonitrile,polyvinyl chloride, poly(vinylidene dichloride), polyethyleneterephthalate, silica, and polyamides such as nylon 6, meta xylyleneadipamide (MXD6) and Nylon 6,6 as well as copolymers thereof, as well asmetal foil layers.

Other additional layers may include one or more layers which arepermeable to oxygen. In one preferred packaging construction, especiallyfor flexible packaging for food, the layers include, in order startingfrom the outside of the package to the innermost layer of the package,(i) an oxygen barrier layer, (ii) a scavenging layer, i.e. thescavenging composition as defined earlier, and optionally, (iii) anoxygen permeable layer. Control of the oxygen barrier property of (i)allows a means to regulate the scavenging life of the package bylimiting the rate of oxygen entry to the scavenging composition (ii),and thus limiting the rate of consumption of scavenging capacity.Control of the oxygen permeability of layer (iii) allows a means to setan upper limit on the rate of oxygen scavenging for. the overallstructure independent of the composition of the scavenging composition(ii). This can serve the purpose of extending the handling lifetime ofthe films in the presence of air prior to sealing of the package.Furthermore, layer (iii) can provide a barrier to migration of theindividual components in the scavenging films or by-products ofscavenging into the package interior. Even further, layer (iii) alsoimproves the heat-sealability, clarity and/or resistance to blocking ofthe multilayer film.

Further additional layers such as adhesive layers may also be used.Compositions typically used for adhesive layers include anhydridefunctional polyolefins and other well-known adhesive layers.

The method of this invention comprises exposing the resultantcomposition to the package cavity having an oxygen sensitive producttherein. A preferred embodiment provides for including a photoinitiatoras part of the subject composition and subjecting a film, layer orarticle having the composition to radiation in order to initiate oxygenscavenging at desired rates. To initiate oxygen scavenging in an oxygenscavenger composition is defined herein as facilitating scavenging suchthat the induction period of oxygen scavenging is significantly reducedor eliminated. As indicated above, the induction period is the period oftime before the scavenging composition exhibits useful scavengingproperties. Further, initiation of oxygen scavenging may also apply tocompositions which have an indeterminate induction period in the absenceof radiation.

The radiation used in this method should be actinic, e.g. ultraviolet orvisible light having a wavelength of about 200 to 750 nanometers (nm),and preferably having a wavelength of about 200 to 600 nm and mostpreferably from about 200 to 400 nm. When employing this method, it ispreferable to expose the oxygen scavenger to at least 1 Joules per gramof scavenging composition. A typical amount of exposure is in the rangeof 10 to 2000 Joules per gram. The radiation can also be an electronbeam radiation at a dosage of about 2 to 200 kilo Gray, preferably about10 to 100 kilo Gray. Other sources of radiation include ionizingradiation such as gamma, X-rays and corona discharge. The duration ofexposure depends on several factors including, but not limited to, theamount and type of photoinitiator present, thickness of the layers to beexposed, thickness and opacity of intervening layers amount of anyantioxidant present, and the wavelength and intensity of the radiationsource. The radiation provided by heating of polyolefin and the likepolymers (e.g., 100-250° C.) during processing does not providetriggering to take effect.

When using oxygen scavenging layers or articles, the exposure toradiation can be during or after the layer or article is prepared. Ifthe resulting layer or article is to be used to package an oxygensensitive product, exposure can be just prior to, during, or afterpackaging. However, in any event, radiation exposure is required priorto using the layer or article as an oxygen scavenger. For bestuniformity of radiation, the exposure should be conducted at aprocessing stage where the layer or article is in the form of a flatsheet.

In order to use the method of this invention in the most efficientmanner, it is preferable to determine the oxygen scavengingcapabilities, e.g. rate and capacity, of the particular oxygen scavengercomposition contemplated for use. To determine the rate of oxygenscavenging, the time elapsed before the scavenger depletes a certainamount of oxygen from a sealed container is measured. In some instancesthe scavenger's rate can be adequately determined by placing a filmcomprising the desired scavenger composition in an air-tight, sealedcontainer of a certain oxygen containing atmosphere, e.g. air whichtypically contains 20.6% oxygen by volume. Then, over a period of time,samples of the atmosphere inside the container are removed to determinethe percentage of oxygen remaining. Usually, the specific rates obtainedwill vary under different temperature and atmospheric conditions.Atmospheres having lower initial oxygen content and/or conducted underlow temperature conditions provide a more stringent test of acomposition scavenging ability and rate. The rates indicated below areat room temperature and one atmosphere of air because they represent theconditions under which, in many instances, the oxygen scavengercomposition and/or layers and articles prepared therefrom will be used.

When an active oxygen barrier is needed, a useful scavenging rate can beas low as 0.05 cc oxygen (O₂) per gram of the copolymer in thescavenging composition per day in air at 25° C. and at 1 atmospherepressure. However, in most instances, it has been found that the presentcompositions have the capability of rates equal to or greater than 0.5cc and even 5 or greater cc oxygen per gram per day. Further, films orlayers comprising the subject composition are capable of a scavengingrate greater than 10 cc oxygen per square meter per day, and can have anoxygen scavenging rate equal to or greater than about 25 cc oxygen persquare meter per day under some conditions. Such rates make those layerssuitable for scavenging oxygen from within a package, as well assuitable for active oxygen barrier applications. Generally, film orlayers generally deemed suitable for use as an active oxygen barrier canhave a scavenging rate as low as one cc oxygen per square meter per daywhen measured in air at 25° C. and 1 atmosphere pressure.

When it is desired to use this method with an active oxygen barrierapplication, the initiated oxygen scavenging activity, in combinationwith any oxygen barriers, should create an overall oxygen transmissionrate of less than about 1.0 cubic centimeters per square meter per dayper atmosphere at 25° C. The oxygen scavenging capacity should be suchthat this transmission rate is not exceeded for at least two days.

Once scavenging has been initiated, the scavenger composition, layer orarticle prepared therefrom, should be able to scavenge up to itscapacity, i.e. the amount of oxygen which the scavenger is capable ofconsuming before it becomes ineffective. In actual use, the capacityrequired for a given application depends on:

(1) the quantity of oxygen initially present in the package,

(2) the rate of oxygen entry into the package in the absence of thescavenging property, and

(3) the intended shelf life for the package.

When using scavengers comprising the subject copolymer containingcomposition, the capacity can be as low as 1 cc oxygen per gram, but canbe 50 cc or higher of oxygen per gram. When such scavengers are in alayer of a film, the layer will preferably have an oxygen capacity of atleast about 250 cc oxygen per square meter per mil thickness and morepreferably at least 1200 cc oxygen per square meter per mil thickness ofsaid layer.

The present composition has been found to provide a film, layer orarticle which substantially retains its physical properties of tensilestrength and modulus even after substantial oxygen scavenging hasoccurred. In addition, the present composition does not provideby-product or effluent which would impart undesired taste, color and/orodor to the packaged product. The term "exposed to the interior" refersto a portion of a packaging article having the subject scavengercomposition which is either directly exposed or indirectly exposed (vialayers which are O₂ permeable) to the interior cavity having oxygensensitive product.

The following examples are given for illustrative purposes only and arenot meant to be a limitation on the invention as defined by the appendedclaims. All parts and percentages are by weight unless otherwise stated.

EXAMPLE 1

Oxygen Scavenging With Poly(ethylene-co-vinylcyclohexene) Films

A copolymer of ethylene and 4-vinyl cyclohexene (7 mole % by NMR) havinglong chain branches (T_(m) =83° C., I₂ =0.67, I₁₀ /I₂ =12.7, Mw=74,000Polydispersity=2.2) was melt compounded at 140° C. with 680 ppm cobaltfrom a commercially available cobalt neodecanoate (Ten-Cem® of OMGInc.), 1000 ppm 4,4'-dimethylbenzophenone, and 500 ppm of a hinderedphenolic antioxidant (Irganox® 1076 Ciba). A film was formed from thiscomposition and a 200 cm² specimen was irradiated (triggered) with UVCradiation to dose of 800 mJ/cm². The specimen was vacuum sealed in abarrier pouch (Cryovac® P640B) and the pouch was inflated with 300 cc of1% oxygen in nitrogen (this oxygen plus residual air in the pouchprovided the initial content of oxygen) and was stored at 4° C. for theduration of the test. Samples of the atmosphere (4 cc) were periodicallywithdraw for oxygen analysis using a MOCON model LC 700F gas analyzerwith the following results:

    ______________________________________                                        Time                                                                          (days after triggering)                                                                       Percent Oxygen                                                ______________________________________                                        0               1.17                                                          1               1.10                                                          2               1.01                                                          5               0.78                                                          8               0.62                                                          14              0.30                                                          22              0.24                                                          ______________________________________                                    

These data clearly show that semi-crystalline, long-chain branched EVCHis suitable for scavenging oxygen even under low temperature conditionsand at low initial oxygen content. Scavenging effects at ambienttemperature and higher initial oxygen content would be even moredramatic.

EXAMPLE 2

A sample of a copolymer compound of ethylene and 4-vinyl cyclohexene(6.5 mole % by NMR) having long chain branches (T_(m) =88° C., I₂ =0.06,I₁₀ /I₂ =21.4, Mw=97,000, Polydispersity=2.2) was melt formulated asdescribed in Example 1, except that the hindered phenolic level was 1360ppm. The sample was irradiated and tested as described in Example 1 withthe following results:

    ______________________________________                                        Time                                                                          (days after triggering)                                                                       Percent Oxygen                                                ______________________________________                                        0               1.12                                                          1               0.91                                                          4               0.43                                                          7               0.23                                                          14              0.10                                                          21              0.06                                                          ______________________________________                                    

These data further show that semi-crystalline, long-chain branched EVCHcan be prepared into a film and is suitable for scavenging oxygen evenunder low temperature conditions and at low initial oxygen content.

What is claimed:
 1. A method of scavenging oxygen by a composition inthe form of a film or packaging material comprising:forming acomposition comprising a mixture of(a) at least one copolymer comprisingunits formed from (i) ethylene and (ii) at least one vinyl unsaturatedalicylic monomer represented by the formula: ##STR4## wherein ##STR5##represents an unsubstituted or substituted C₆ -C₁₂ non-aromaticethylenic unsaturated alicyclic group, said copolymer having unitsformed from said at least one vinyl unsaturated alicyclic monomer infrom 1 to 35 mole percent of said copolymer, having long chain branchesof at least 6 carbon atoms present in an amount to cause said copolymerto have a melt flow index ratio (I₁₀ /I₂) of at least about 8, andhaving a polydispersity (Mw/Mn) of about 1.5 to 5; and (b) a transitionmetal catalyst; shaping the formed composition to form at least part ofa packaging material or film; and exposing the package material or filmto actinic radiation having a wavelength of between 200 and 750 nm or toelectron beam radiation of at least about 2 kilo Gray.
 2. The method ofclaim 1 wherein the copolymer further comprises units derived from amonomer selected from a C₃ -C₂₀ alpha-olefin, cycloolefin,non-conjugated dienes and mixtures thereof.
 3. The method of claim 1wherein said mixture further contains at least one photoinitiatorcompound.
 4. The method of claim 2 wherein said mixture further containsat least one photoinitiator compound.
 5. The method of claim 1 whereinthe mixture further comprises at least one diluent polymer.
 6. Themethod of claim 2 wherein the mixture further comprises at least onediluent polymer.
 7. The method of claim 3 wherein the mixture furthercomprises at least one diluent polymer.
 8. The method of claim 4 whereinthe mixture further comprises at least one diluent polymer.
 9. Themethod of claim 1, 2, 3, 4, 5, 6, 7 or 8 wherein the at least one vinylunsaturated alicyclic desired units are present in said copolymer infrom 1 to 15 mole percent of said copolymer.
 10. The method of claim 9wherein at least one of said vinyl unsaturated alicyclic units of saidcopolymer has one ethylenic carbon--carbon group within said alicyclicgroup.
 11. The method of claim 9 wherein the copolymer is derived fromethylene and vinyl cyclohexene.
 12. The method of claim 11 wherein thevinyl cyclohexene is present in from 1 to 10 molar percent.
 13. Themethod of claim 9 wherein the copolymer has a polydispersity of at leastabout 1.5 to 5 and a melt flow index ratio (I₁₀ /I₂) of at least about8.
 14. A packaging article in the form of a rigid, semi-rigid orflexible article having at least one layer, wherein at least one of saidlayer being exposed to the internal cavity of said packaging article andcomprising the packaging material or film of claim 1, 2, 3, 4, 5, 6, 7or
 8. 15. A packaging article in the form of a rigid, semi-rigid or filmarticle having at least one layer, wherein at least one of said layerbeing exposed to the internal cavity of said packaging article andcomprising the packaging material of film of claim
 9. 16. A packagingarticle in the form of a rigid, semi-rigid or film article having atleast one layer, wherein at least one of said layer being exposed to theinternal cavity of said packaging article and comprising the packagingmaterial or film of claim
 10. 17. A packaging article in the form of arigid, semi-rigid or film article having at least one layer, wherein atleast one of said layer being exposed to the internal cavity of saidpackaging article and comprising the packaging material or film of claim11.
 18. A packaging article in the form of a rigid, semi-rigid or filmarticle having at least one layer, wherein at least one of said layerbeing exposed to the internal cavity of said packaging article andcomprising the packaging material or film of claim
 12. 19. A packagingarticle in the form of a rigid, semi-rigid or film article having atleast one layer, wherein at least one of said layer being exposed to theinternal cavity of said packaging article and comprising the packagingmaterial or film of claim 13.